Resnet18 is predicting incorrect label


#1

I wrote a following script to predict image label for resent 18.

import mxnet as mx
model_name = 'resnet-18'
path='http://data.mxnet.io/models/imagenet/resnet/'
    [mx.test_utils.download(path+'18-layers/resnet-18-symbol.json'),
     mx.test_utils.download(path+'18-layers/resnet-18-0000.params'),
     mx.test_utils.download(path+'synset.txt')]
sym, arg_params, aux_params = mx.model.load_checkpoint(model_name, 0)
mod = mx.mod.Module(symbol=sym, context=mx.cpu(), label_names=None)
mod.bind(for_training=False, data_shapes=[('data', (1,3,224,224))], 
         label_shapes=mod._label_shapes)
mod.set_params(arg_params, aux_params, allow_missing=True)
with open('synset.txt', 'r') as f:
    labels = [l.rstrip() for l in f]

%matplotlib inline
import matplotlib.pyplot as plt
import cv2
import numpy as np
# define a simple data batch
from collections import namedtuple
Batch = namedtuple('Batch', ['data'])

def get_image(url, show=False):
    # download and show the image
    fname = mx.test_utils.download(url)
    img = cv2.cvtColor(cv2.imread(fname), cv2.COLOR_BGR2RGB)
    if img is None:
         return None
    if show:
         plt.imshow(img)
         plt.axis('off')
    # convert into format (batch, RGB, width, height)
    img = cv2.resize(img, (224, 224))
    img = np.swapaxes(img, 0, 2)
    img = np.swapaxes(img, 1, 2)
    img = img[np.newaxis, :]
    return img

def predict(url):
    img = get_image(url, show=True)
    # compute the predict probabilities
    mod.forward(Batch([mx.nd.array(img)]))
    prob = mod.get_outputs()[0].asnumpy()
    # print the top-5
    prob = np.squeeze(prob)
    a = np.argsort(prob)[::-1]
    for i in a[0:5]:
        print('probability=%f, class=%s' %(prob[i], labels[i]))
predict('http://writm.com/wp-content/uploads/2016/08/Cat-hd-wallpapers.jpg')

Output

probability=0.244390, class=n01514668 cock
probability=0.170342, class=n01514752 gamecock, fighting cock
probability=0.145019, class=n01495493 angel shark, angelfish, Squatina squatina, monkfish
probability=0.059832, class=n01540233 grosbeak, grossbeak
probability=0.051555, class=n01517966 carinate, carinate bird, flying bird

I am getting completly wrong output.

Same code I tried with Resent 152., Output I got is correct

probability=0.692327, class=n02122948 kitten, kitty
probability=0.043847, class=n01323155 kit
probability=0.030002, class=n01318894 pet
probability=0.029693, class=n02122878 tabby, queen
probability=0.026972, class=n01322221 baby

#2

You need to normalize the image before prediction. Checkout this: https://mxnet.incubator.apache.org/api/python/gluon/model_zoo.html#module-mxnet.gluon.model_zoo.vision

image = image/255
normalized = mx.image.color_normalize(image,
                                      mean=mx.nd.array([0.485, 0.456, 0.406]),
                                      std=mx.nd.array([0.229, 0.224, 0.225]))